6 
Transactions of the JRoyal Society of South Africa. 
As will be seen from the latter formula, the substance is the ortho- 
carboxylic acid of f uchsone, the latter being the inner-anhydride of para-oxy- 
triphenylcarbinol, and its systematic name being diphenyl - methylene- 
quinone (" diphenyl - chinomethan " in Germany). The centre of its 
absorption band lies at about X560 (frequency 17'86). Fuchsone itself 
cannot be investigated by this method, since it is a neutral body giving no 
colour in alkali, though itself coloured (orange). 
Another related compound of simple constitution may be taken next, 
although it is not a phthalein — viz. benzaurine or 4'-oxyfuchsone 
__ >C<->:0 
<_x 
This differs chemically from the preceding compound in having no ortho- 
COoNa group, but has a para-ONa group instead (both phenyl groups of 
the fuchsone molecule having the same function). This alkaline group 
confers solubility in water, with colour, as m the foregoing case, but the 
colour is now a reddish-purple with absorption-band at X 570 (frequency 
17'56). The addition of strong NaOH to benzaurine first deepens the colour 
to purple (absorption-band A 585), probably due to the formation of 
\_/ 
and, on warming, bleaches the colour owing to the destruction of the quino- 
noid ring to form 
^C(ONa)— <^ ^ONa 
\ X 
or the trisodium salt of dioxytriphenylcarbinol, by migration of an — ONa 
group from the end to the middle of the system. The same behaviour is 
shown by monoxydiphenylphthalide in an exaggerated degree, only a slight 
alkalinity sufficing to bleach it. 
The effect of the addition of a second para-OH (or — ONa) group to 
the molecule may next be studied. Ordinary phenolphthalein is the para- 
OH derivative of monoxydiphenylphthalide, and ordinary aurine is the 
corresponding OH derivative of benzaurine. The effect is surprising, since 
in both cases the absorption-band moves down the spectrum into the green, 
